A Philippine court has sentenced an Indonesian and two Filipino Muslim militants to death for their role in the bombing of a Manila bus last February that killed four people and wounded dozens.

The Abu Sayyaf group, which is linked to the al-Qaida terror network, claimed responsibility for the February 14 bus attack, as well bombings in two southern towns the same day.

The Makati City court in Manila, convicted Filipinos Gamal Baharan and Angelo Trinidad, who are suspected members of the Abu Sayyaf group and who admitted to multiple murder charges. The court also convicted an Indonesian, named only Rohmat, who is described as a leader of the regional terrorist group, Jemaah Islamiyah. Rohmat pleaded not guilty.

Authorities say several dozen Indonesian militants have been involved in training local guerrillas in the southern Philippines in bomb-making and plotting attacks. The island of Mindanao is a key area for such training. Ramon Casiple, of the Institute for Political and Electoral reforms, says the pattern is clear.

"It has been confirmed time and again, whenever incidents, including, of course, our own incidents of kidnapping and terrorism even here in Manila, are traceable to Mindanao-based training, which is given, not only to Filipinos, but Indonesians and even Malaysians," he said.

Mr. Casiple says Mindanao is vulnerable to such activities because it is politically unstable, and has a long shoreline that is difficult to police.

"The problem actually is that Mindanao is a war zone," he explained. "We have an internal conflict there. The hold of the government over certain areas of Mindanao is really not that solid. It's a porous area. People from Indonesia and Malaysia can go to provinces in Mindanao through the seas."

Mindanao is home to the bulk of the Muslim community in the Philippines, which has a predominantly Christian population. It is one of the poorest areas in the country. Islamic militants have fought a separatist war there for three decades, although recent peace negotiations have been making headway.

Analysts say Abu Sayyaf and Jemaah Islamiyah have capitalized on political instability and discontent on the island to strengthen their ranks.

Although Abu Sayyaf says it is fighting to create a Muslim homeland, it is best known for a series of dramatic kidnappings for ransom and murders. Jemaah Islamiyah, which is based in Indonesia, has been implicated in several deadly bombings in Indonesia, including two attacks on the tourist island of Bali.

The United States has provided aid and military training to the Philippines over the past several years, as Manila tries to crack down on militant groups.

The last execution in the Philippines was carried out in January 2000. However, Chief Public Attorney Pairsida Acosta says death sentences are handed down monthly for crimes such as murder and child rape.